Multiple hearth refractory furnace



1964 H. J. HARTLEY ETAL 3, 31,919

MULTIPLE HEARTH REFRACTORY FURNACE Filed Oct. 5. 1961 3 Sheets-Sheet 1IE E L INVENTORS Henry J l/orf/ey 45/7/57 J. Ho/fl'nyswar/h 147' 7 ORA/EX5 United States Patent F MULTIILE HEARTH EIRACTORY Henry .I. Hartley,Les Angcles, and Ashley .I. Hollingsworth, Atherton, Caiifu, assignorsto Bartiett-Snow- Pacific, ind, San Francisco, Calif, a corporation ofCaiifornia Filed Get. 5, 1961, Ser. No. 143,175 5 Claims. (Ci. 263-22)This invention relates to furnaces and more particularly to furnaces orkilns of the multiple hearth construction.

In multiple hearth furnaces constructed in the past, the generalarrangement has been a stacked plurality of stationary hearths eachhaving a central opening through which a central shaft is rotatablypassed. Each of the stationary hearths also includes openings in thefloors thereof through which material to be processed may be passeddownwardly from one hearth to the next. Rabble arms are afixed to thecentral shaft at the level of each hearth. Upon rotation of the shaftand rabble arms, the material to be processed is rabbled across thehearth toward the openings therein to pass downwardly to the next lowerhearth.

Due to the strength required for the central shaft and rabble arms, thematerial used in the past for the construction of these elements hasnecessarily been steel. The use of steel has limited the maximumtemperatures which may be employed in such furnaces. Although variousmeans have been considered and utilized for cooling the shaft and therabble arms. Such means usually comprise forcing cool air throughcentral openings in the shaft and rabble arms. However, even with thecooling devices of the prior art, maximum temperature in furnaces ofthis type has been in the neighborhood of 1860" or 1900 F.

In view of the above it is an object of this invention to provide animproved multiple hearth furnace or kiln.

It is a more particular object of this invention to provide a multiplehearth furnace having improved maximum temperature characteristics.

It is still another object of this invention to provide a multiplehealth furnace with modular construction wher in the furnace capacitymay be easily altered.

It is still another object of this invention to provide a multiplehearth furnace wherein the number of required burners per hearth isreduced.

It is still another object of this invention to provide a multiplehearth furnace wherein close temperature control may be operated.

It is a further object of this invention to provide a furnace having theabove mentioned characteristics, wherein the gaseous atmosphere withinthe furnace can be easily controlled.

It is another object of this invention to provide a multiple hearthfurnace wherein the interior of the furnace is sealed with respect toits exterior.

It is still another object of this invention to provide a multiplehearth employing rabble arms and rabble teeth which may be adjusted orreplaced while furnace is in operation.

It is still another object of this invention to provide a multiplehearth furnace of the aforementioned characteristics whereby therabbling speed of each individual hearth may be separately adjusted.

It is still another object of this invention to provide a multple hearthfurnace of the aforementioned characteristics which employs overloadprotection for the forces exerted by the rabble arms themselves.

It is still another object of this invention to provide a multiplehearth furnace which incorporates a simple apron feed wherein materialmay be supplied to the furnace with an air seal.

3,131,919 Patented May 5, 1%54 It is still another object of thisinvention to provide a multiple hearth furnace wherein the rabble armsare secured at both ends, thereby providing increased strength.

it is still another object of this invention to provide a multiplehearth furnace of the aforementioned characteristics which may bedisassembled and re-assembled rapidly in order to facilitate shipping,cleaning and repair.

These and other objects and features of the invention will become moreclearly apparent upon a review of the following description inconjunction with the drawing, in which:

FIGURE 1 is an elevational view of a furnace in accordance with oneembodiment of this invention;

FIGURE 2 is a top plan view of the furnace shown in FIGURE 1 with theroof member removed;

FIGURE 3 is a composite elevational cross sectional view of the furnaceshown in FIGURES 1 and 2;

FIGURE 4 is a side elevational view of a rabble arm assembly inaccordance with another embodiment of this invention;

FIGURE 5 is a sectional view taken along the line 5-5 of FIGURE 4;

FIGURE 6 is a side elevational view of a rabble arm in accordance withstill another embodiment of this invention;

FIGURE 7 is a sectional view taken along the line 7--7 of FIGURE 6;

FIGURE 8 is a plan view of a rabble arm in accordance with a furtherembodiment of this invention; and

FIGURE 9 is an elevational view of a tooth used with the arms of FIGURE8.

In general, the above objects and features of this invention areaccomplished by providing alternate rotating hearth sections andstationary ring sections stacked to form a furnace which may have avariable number of hearths. Rabble arms with depending teeth, formed ofrefractory material, are supported by the stationary ring sections. Thematerial to be processed is supported by the rotating hearth while thestationary arms and teeth serve to rabble the material across thehearths towards openings in the floor thereof through which the materialis passed to the next lower hearth.

Referring particularly to FIGURES l, 2 and 3 of the drawing, uprightsupport members 11 are secured to a base member on floor 13. Ringsections 15 are removably secured to thesupport members 11 by means ofthe flanges 17 and 19 which are secured to each other by means of boltsor the like, whereby they may be easily removable. Flanges 17 and 19 maybe secured to the respective supports 11 and sections 15 by welding orother suitable means.

Each of the stationary ring sections 15 is annular in form and comprisesan inner shell 21 of refractory material and an outer shell 23 of heatinsulating material. In addition a thin annular band 25, which may be ofsteel, surrounds the shell 23.

Also secured to each of the stationary ring sections 15 are a pluralityof rollers or bearings 31 about the outer periphery thereof. The rollers31 may be omitted on the uppermost stationary ring sections for reasonswhich will become apparent hereinafter. Conveniently, the upperextremity of the rollers 31 may extend above its asso ciated ringsection 15, although this is not entirely necessary.

Also secured to the upright supports 11 is a bottom member 33 secured tothe support member by flanges similar to those associated with thestationary ring sections. The member 33, like the stationary section 15,includes a plurality of rollers or bearings 37.

The rollers 31 and 37 serve to rotatably support the various hearthsections 39. The hearth sections 39 each include a hearth floor 41formed or" refractory material surrounded by an annular formation 43 ofinsulating material.

' On the upper face and near the outer periphery of each of thestationary sections 15, bottom sections 33, and hearth sections 39,there is included an annular well 45 which is filled with a sealingmaterial such as sand. Annular sealing members 47 are formed on thelower face of each of the ring sections 15 and hearth sections 39 inregistry with the annular wells of the adjacent sections to form a gasseal between the inside and outside of the overall furnace. A pluralityof plowing pins 48 are disposed about the annular sealing member'47 andserve to continually break up the sealing material such that a hardenedor packed pocket cannot be formed. Thus, the sealing member and thesealing material form a continual and effective gas seal.

Each ofthehearth sections 39 includes an outer band 49 which may beofsteel, to which is secured a radially extending annular flange E. Theflange 51 cooperates with the rollers 31 and 37 to provide spacedsupport for the hearth sections 39 with respect to the stationary ringsections 15. Thus, it is seen that the hearth sections 39 maybe rotatedwith respect to the ring sections onthe rollers 31 and 37.

Means for rotating the hearth sections -3 include motive means 53operatively coupled to a vertical shaft 55.

7 One of the upright support members 11 may rotatably re-,

tain the shaft 55 by means of the bearings 57. Drive gears or sprockets5% may be secured to the shaft 55 by means of sheer pins 61 or by anoverload slip clutch. Drive chains '63 cooperate with the sprockets 5?and extend about the rotatable hearth 39. The hearth member 3? mayinclude radially extending pins or the like to provide a positivedriving relationship between the chain 63 and the hearth sectionsthemselves. it is apparent that the diameter of individual sprockets 59may be varied whereby the relative rotational velocity of the individualhearths with respect to each other may be varied. In addition, overallspeed adjustment may be accomplished by means of a variable speed drive65 associated with the motive means 53 and the shaft 55.

It is apparent from the construction of the furnace thus far describedthat the number of hearths may be simply varied, even after thestructure is completed, by adding or removing individual stationary ringsections 15 and associated hearth sections 3? to or from the upright Isupport members 11.

Upon the uppermost stationary ring section 15 there is placed a top orroot member 67 which includes an un der surface'69 of refractorymaterial as well as an annular portion 71 and top portion 73 of heatinsulating material. Heat seal means is provided between'the uppermost,ring section 15 and the top of roof member '67 As noted'particularly inFIGURE 3 each of the hearth floors 41 includes at least one openingtherein for passage of the material to be processed from one hearth tothe next lower hearth. In the embodiment shown in FIGURE 3 the upper andlowermost hearth 'fioors ll include a central opening 75 while thecentral hearth iloor 41includes peripheral openings 77. If .additionalhearths arev used central openings 75 and peripheral openings 77 will.be alternatively employed whereby rabbling may occur in one hearth fromthe periphery to the center and on the subsequent hearth from the centerto the periphery etc.

It is convenient that the uppermost hearth employ a centralopening 75whereby apron feed means may be employed at the periphery. Thus, a pipe79 is located near the outer periphery of the uppermost hearth. The pipe79 is passed through the roof section 67 and exends downwardly into thefurnace in close proximity with the uppermost floor section 41. Thus, asthe uppermost hearth floor 41 is rotated, it cooperates with the pipe 79to form an apron feed. The material to be processed is passed throughthe pipe 79 and distributed about the periphery of the uppermost door41. In addition, with the the removal means cooperates with the outlet 37 to form.

ary ring sections employs a plurality of rabble arms 81 I arranged asshown more clearly in FIGURE 2. Each of the rabble arms 81 isconstructed of refractory material and includes a stem portion 83 anddepending teeth 85. The arms may be inserted into the furnace throughcircumferentially spaced openings 87 in each of the stationary ringsections 15. The size ofthe openings 87 are proportioned such that therabble arms may be passed through while the depending teeth are in arelatively horizontal plane. The arms are subsequently rotated such thatthe teeth 85 extend downwardly.

As notedparticularly in FIGURES 2 and 3 each of the rabble arms extendinwardly to the center of the'frame and is keyed as at 89 whereby theyare joined together to form a relatively rigid armsupported at each end.In addition each of the stationary ring sections may include a burner91. Since the hearths in this case are rotatable, a single burner maybe' employed at each hearth to heat all of the material to be processed.In particularly large furnaces it maybe desirable to provide additionalburners butin any case the number of burners required will be less thanordinarily required for station-' ary hearth furnaces since the materialis continually passed beneath the stationary burners.

7 Doors 93 may be provided whereby inspection of furnace operation maybe accomplished. Additionally a spudding tool may be easily used againstthe moving hearth through the door 93 without stopping the furnace. I V

A flue 95 isprovided in the top section 67 whereby the gases'developedin the furnace may be removed. Also a material outlet 97 is provided inthe bottom section 33 in registry with the central opening inthelowernlost hearth floor 41. The material maybe received from theoutlet 97 and distributed in a convenient manner Preferably,

an'apron outlet whereby a gas seal is provided by the processed materialitself.

In the operation of the furnace, the material to be processed'is passedthrough the apron feed 79' onto the outer periphery of uppermost hearthfloor 41. The rotation of the hearth causes the material to be spreadabout the uppermost door. with the uppermost floor cause the material tobe removed centrally toward the opening 75 whereby it is dropped to thenext lower hearth floor 4-1, at the next lower floor the rabble armshave teeth disposed at an opposite pitch to those associated with thefirst hearth and thus cause.

the material to be rabbled outwardly to the opening 77 where it isdropped to the next lower hearth floor 41.

. The cycle is repeated until the material is rabbled toward thelowermost opening 75 and through the outlet 7.

Referring particularly to the embodiment shown in.

FIGURES d and 5 therabble armsextend not only to the center of thehearth but completely across whereby it may be secured at each wall.With this construction a single arm may be employedfor each hearth. Asseen in FIGURE 5 a pair of bars 101 are employedand may be extendedentirely across the furnace and secured at the outer walls thereof. Thebars rill are spaced so 'asto provide anopening 1% through which therabble teeth Hi5 may pass. The teeth 1%5 include head portions 107.

which rest upon the bars 101 and may be of such dimension to provide therequ red spacing between teeth when in abutting relationship as shown at199; Thus, it is seen that the teeth 1435 may be readily removed fromthe bars Trill. Broken teeth may be replaced by merely removing the sameand sliding another tooth along the bars it'll.

Referring more particularly'to FIGURES, it is seen that the bars 161 mayinclude a centrally disposed metal Stationary rabble arms associatedpipe 111 surrounded by refractory material. The metal portion mayprovide additional strength and may be cooled by the passage of airtherethrough. if desired the pipe can be eliminated and the entirestructure fabricated from refractory material. in any event no metalsurface is directly exposed to the furnace heat.

Referring to FIGURES 6 and 7 in the form of a tooth assembly, a rabblearm is shown. Here again, the arm extends entirely across the furnaceand the ends are secured at the outer walls of the furnace.

In this case a plurality of teeth 113, each having lzeyed surfaces 115,are held together by axial compression of the tooth assembly. An opening117 through each tooth may be used in conjunction with a rod (not shown)passed therethrough to hold the teeth in their assembled relationshipwhen the axial compressi e force is removed. Thus, to replace a brokentooth, a rod is passed through the opening 117 of all the teeth, thecompressive force is removed and a new tooth is passed along the rodinto keyed relationship with the other teeth. The compressive force isreturned and the rod subsequently removed.

Referring to FZGURES 8 and 9 another rabble arm is shown wherein aplurality of teeth 119 are mounted on a central shaft 121. As can betterbe seen in ElGUnE the teeth 119 are loca d on the shaft 121 at an acuteangle with the shaft axis. Thus, the raobdng pitch of the arm isdetermined. Each of the teeth includes a mounting head 123 having aseries of concentric grooves 125 on one face and a series of concentricridges (not shown) on the opposite face in registry with grooves.

The shaft 1 1 includes a wedge shaped stop member 127 secured at one endby welding or otherwise, and the plurality of teeth 119 are fitted overthe shaft in stacked relationship adjacent the stop member 127. One ormore tapered Washers 129 of the Belville type are fitted next over theshaft and the assembly is tightened together by a threaded nut 131.

Due to the action of intermeshed grooves 125 and ridge the assembly isheld intact even with wide temperature variations and the consequentcracking in the teeth themselves.

Thus, it is seen that an improved multiple hearth furnace is providedwherein high temperatures may be employed. Since the construction of theinterior of the furnace is refractory material, particularly hightemperatures may be employed in the neighborhood of 2500 to 2600 F. andabove. If desired the rabble arms as described hereinabove may includecentral pipe portions for additional strength. Coolin fluids may bepassed through the pipe portions to reduce the temperature destructionthereof.

The furnace retains the features of precise temperature control, evenheat distribution and high heat recovery which are well known in rotaryhearth furnaces. At the same time much higher temperatures may beemployed which in the past have required rotary kilns.

Due to the combination of the improved temperature characteristic alongwith rabbling actions, processes never before achieved may be performed.One important process made feasible by this novel furnace is therecovery of lime [C210] from lime sludge [Ca(OH)]. Other processesinclude oxidation of certain metals requiring high heat. In addition,since the internal atmosphere of the furnace is controlled by sand sealsbetween movable members, and by material seals at the apron feed anddischarge, the reduction of metallic oxides is greatly facilifated.

We claim:

1. A multiple hearth furnace comprising a plurality of vertical supportmembers, a plurality of stationary annular ring sections rigidly butremovably secured to said support members in vertically spacedrelationship, each of said ring sections defining a central opening, ahearth section rotatably supported below and extended across the openingof each of said stationary ring sections, said hearth sections beingsupported entirely externally of the hearth and said stationary ringsections, motive means for rotating said hearth sections relative tosaid stationary ring sections and rabble arm means supported by saidstationary ring sections and extending inwardly thereof, said rabble armmeans including a pair of transversely spaced bars extending entirelyacross the interior of the furnace, and teeth removably disposed betweensaid bars.

2. A furnace as defined in claim 1 wherein said bars are formed entirelyof ceramic refractory material.

3. A furnace as defined in claim 1 wherein said bars include a metalpipe and refractory material, the outer surface of said metal pipe beingentirely surrounded by said refractory material.

4-. A multiple hearth furnace comprising a plurality of vertical supportmembers, a plura ity of stationary annular ring sections rigidly butremovably secured to said support members in vertically spacedrelationship, each of said ring sections defining a central opening, ahearth section rotatably supported below and extended across the openingof each of said stationary ring sections, said hearth sections beingsupported entirely externally of the hearth and said stationary ringsections, motive means for rotating said hearth sections relative tosaid stationary ring sections, rabble arm means supported by saidstationary ring sections and extending inwardly thereof, said rabble armmeans comprising a tooth assembly, said tooth assembly including aplurality of separate teeth each having key means on opposed side facesthereof said teeth being disposed adjacent each other with the key meansof adjacent teeth being keyed together, and means for compressivelyurging said teeth together whereby the teeth are retained in anassembled condition.

5. A furnace as defined in claim 4 wherein each of said teeth include acentral opening communicating with each of said opposed faces, a rodadapted to be passed through said opening whereby temporary retention ofthe teeth in assembled condition may be maintained.

References Cited in the file of this patent UNITED STATES PATENTS

1. A MULTIPLE HEARTH FURNACE COMPRISING A PLURALITY OF VERTICAL SUPPORTMEMBERS, A PLURALITY OF STATIONARY ANNULAR RING SECTIONS RIGIDLY BUTREMOVABLY SECURED TO SAID SUPPORT MEMBERS IN VERTICALLY SPACEDRELATIONSHIP, EACH OF SAID RING SECTIONS DEFINING A CENTRAL OPENING, AHEARTH SECTION ROTATABLY SUPPORTED BELOW AND EXTENDED ACROSS THE OPENINGOF EACH OF SAID STATIONARY RING SECTIONS, SAID HEARTH SECTIONS BEINGSUPPORTED ENTIRELY EXTERNALLY OF THE HEARTH AND SAID STATIONARY RINGSECTIONS, MOTIVE MEANS FOR ROTATING SAID HEARTH SECTIONS RELATIVE TOSAID STATIONARY RING SECTIONS AND RABBLE ARM MEANS SUPPORTED BY SAIDSTATIONARY RING SECTIONS AND EXTENDING INWARDLY THEREOF, SAID RABBLE ARMMEANS INCLUDING A PAIR OF TRANSVERSELY